This component doesn't update even tho props change.
prop row is an object.
console.log("row", row") does work. and get correct data also console.log("Data", data)
import React, {useState, useEffect} from "react";
const Form = ({row}) => {
const [data, setData] = useState(row);
console.log("row", row); //consoleLog1
useEffect(() => {
setData(row);
}, [row]);
return (
<>
{Object.getOwnPropertyNames(data).map((head) => {
console.log("Data", data);//consoleLog2
return <input type="text" name={head} defaultValue={data[head] == null ? "" : data[head]} />;
})}
</>
);
};
export default Form;
Update
changing return to <input value={data["ID"}> . and it does update .
is there any way to create a form using looping object's properties?
The defaultValue prop is used for uncontrolled components. It sets the starting value, and then it's out of your hands. All changes will be handled internally by input. So when you rerender and pass in a new defaultValue, that value is ignored.
If you need to change the value externally, then you either need to unmount and remount the components, which can be done by giving them a key which changes:
<input key={data[head].someUniqueIdThatChanged}
Or you need to use the input in a controlled manner, which means using the value prop instead.
value={data[head] == null ? "" : data[head]}
For more information on controlled vs uncontrolled components in react, see these pages:
https://reactjs.org/docs/forms.html#controlled-components
https://reactjs.org/docs/uncontrolled-components.html
P.S, copying props into state is almost always a bad idea. Just use the prop directly:
const Form = ({row}) => {
return (
<>
{Object.getOwnPropertyNames(row).map((head) => {
return <input type="text" name={head} defaultValue={row[head] == null ? "" : row[head]} />;
})}
</>
);
}
I'm trying to display the value of my inputs from a from, in a list. Everytime I hit submit, I expect that it should display the inputs in order.
The problem I'm having is that when I try to submit my form and display inputs in a list, it display an empty value first. On the next submit and thereafter, it displays the previous value, not the new one on the input field.
There's also an error message but i'm not understanding how to relate it to the problem. It's a warning message regarding controlled/uncontrolled components.
I've tried to add if statements to check for empty values in each functions but the problem persists.I've tried to manage the error massage by being consistent with all input to be controlled elements using setState, but nothing works.
I looked through todo list examples on github. I guess i'm trying to keep it in one functional component versus multiple ones, and I'm not using class components. I tried to follow the wesbos tutorial on Javascript 30 day challenge, day 15: Local Storage and Event Delegation. I'm trying to use React instead of plain JS.
Here's what my component looks like.
import React, { useEffect, useState } from "react";
import "../styles/LocalStorage.css";
export const LocalStorage = () => {
const [collection, setCollection] = useState([]);
const [value, setValue] = useState();
const [item, setItem] = useState({ plate: "", done: false });
const [display, setDisplay] = useState(false);
//set the value of the input
const handleChange = (e) => {
if (e.target.value === "") return;
setValue(e.target.value);
};
const handleSubmit = (e) => {
e.preventDefault();
if (value === "" || undefined) return;
setItem((prevState) => {
return { ...prevState, plate: value };
});
addItem(item);
setDisplay(true);
setValue("");
};
const addItem = (input) => {
if (input.plate === "") return;
setCollection([...collection, input]);
};
return (
<div>
<div className="wrapper">
<h2>LOCAL TAPAS</h2>
<ul className="plates">
{display ? (
collection.map((item, i) => {
return (
<li key={i}>
<input
type="checkbox"
data-index={i}
id={`item${i}`}
checked={item.done}
onChange={() =>
item.done
? setItem((state) => ({ ...state, done: false }))
: setItem((state) => ({ ...state, done: true }))
}
/>
<label htmlFor={`item${i}`}>{item.plate}</label>
</li>
);
})
) : (
<li>Loading Tapas...</li>
)}
</ul>
<form className="add-items" onSubmit={handleSubmit}>
<input
type="text"
name="item"
placeholder="Item Name"
required
value={value}
onChange={handleChange}
/>
<button type="submit">+ Add Item</button>
</form>
</div>
</div>
);
};
Since the setState function is asynchronous, you cannot use the state value item right after you fire the setItem(...). To ensure you get the latest value for your addItem function:
setItem((prevState) => {
const newItem = { ...prevState, plate: value };
addItem(newItem); // Now, it's getting the updated value!
return newItem;
});
And regarding the controlled and uncontrolled components, you can read the docs about it here. To fix your problem, you can initialize the value state with an empty string:
const [value, setValue] = useState('');
I'm trying to find a neater way to handle this pattern I keep coming across with react when handling changes for form fields.
For each element of my form object that I handle a change in value for I find myself replicating this pattern quite a bit with the setter function of useState(). I've tried a couple of things like creating shallow copies of the formState and mutating that but the only way I can really get things to work is with the bellow pattern which feels a little repetitive.
const handleTitle = evt => {
props.setFormState({
title: evt.target.value,
bio: props.formState.bio,
formExpertise: props.formState.formExpertise,
formExpertiseYears: props.formState.formExpertiseYears
});
};
If you want to include this.props.formState you can spread the object into the new state. Further, you can use the input’s name as the state key so you don’t have to rewrite this for every input:
props.setFormState({
...this.props.formState, // copy props.formState in
[evt.target.name]: evt.target.value // use input name as state key
});
Suggestion:
You might consider moving the state merging up into the parent component:
// parent component
const [formState, setFormState] = React.useState({});
const onFieldChange = (field, value) => {
setFormState({
...formState,
[field]: value
});
}
return (
<MyFormComponent
formState={formState}
onFieldChange={onFieldChange}
/>
);
Each input can then invoke onFieldChange with the field name and value without concerning itself with the rest of the state:
function MyFormComponent ({onFieldChange}) {
const handler = ({target: {name, value}}) => onFieldChange(name, value);
return (
<div>
<input name="title" value={formState.title} onChange={handler} />
<input name="bio" value={formState.bio} onChange={handler} />
<input name="expertise" value={formState.expertise} onChange={handler} />
</div>
);
}
I have a simple react component with the form which I believe to have one controlled input:
import React from 'react';
export default class MyForm extends React.Component {
constructor(props) {
super(props);
this.state = {}
}
render() {
return (
<form className="add-support-staff-form">
<input name="name" type="text" value={this.state.name} onChange={this.onFieldChange('name').bind(this)}/>
</form>
)
}
onFieldChange(fieldName) {
return function (event) {
this.setState({[fieldName]: event.target.value});
}
}
}
export default MyForm;
When I run my application I get the following warning:
Warning: MyForm is changing an uncontrolled input of type text to be
controlled. Input elements should not switch from uncontrolled to
controlled (or vice versa). Decide between using a controlled or
uncontrolled input element for the lifetime of the component
I believe my input is controlled since it has a value. I am wondering what am I doing wrong?
I am using React 15.1.0
I believe my input is controlled since it has a value.
For an input to be controlled, its value must correspond to that of a state variable.
That condition is not initially met in your example because this.state.name is not initially set. Therefore, the input is initially uncontrolled. Once the onChange handler is triggered for the first time, this.state.name gets set. At that point, the above condition is satisfied and the input is considered to be controlled. This transition from uncontrolled to controlled produces the error seen above.
By initializing this.state.name in the constructor:
e.g.
this.state = { name: '' };
the input will be controlled from the start, fixing the issue. See React Controlled Components for more examples.
Unrelated to this error, you should only have one default export. Your code above has two.
When you first render your component, this.state.name isn't set, so it evaluates to undefined or null, and you end up passing value={undefined} or value={null}to your input.
When ReactDOM checks to see if a field is controlled, it checks to see if value != null (note that it's !=, not !==), and since undefined == null in JavaScript, it decides that it's uncontrolled.
So, when onFieldChange() is called, this.state.name is set to a string value, your input goes from being uncontrolled to being controlled.
If you do this.state = {name: ''} in your constructor, because '' != null, your input will have a value the whole time, and that message will go away.
Another approach it could be setting the default value inside your input, like this:
<input name="name" type="text" value={this.state.name || ''} onChange={this.onFieldChange('name').bind(this)}/>
I know others have answered this already. But a very important factor here that may help other people experiencing similar issue:
You must have an onChange handler added in your input field (e.g. textField, checkbox, radio, etc). Always handle activity through the onChange handler.
Example:
<input ... onChange={ this.myChangeHandler} ... />
When you are working with checkbox you may need to handle its checked state with !!.
Example:
<input type="checkbox" checked={!!this.state.someValue} onChange={.....} >
Reference: https://github.com/facebook/react/issues/6779#issuecomment-326314716
Simple solution to resolve this problem is to set an empty value by default :
<input name='myInput' value={this.state.myInput || ''} onChange={this.handleChange} />
One potential downside with setting the field value to "" (empty string) in the constructor is if the field is an optional field and is left unedited. Unless you do some massaging before posting your form, the field will be persisted to your data storage as an empty string instead of NULL.
This alternative will avoid empty strings:
constructor(props) {
super(props);
this.state = {
name: null
}
}
...
<input name="name" type="text" value={this.state.name || ''}/>
I had the same problem.
the problem was when i kept the state info blank
const [name, setName] = useState()
I fixed it by adding empty string like this
const [name, setName] = useState('')
In my case, I was missing something really trivial.
<input value={state.myObject.inputValue} />
My state was the following when I was getting the warning:
state = {
myObject: undefined
}
By alternating my state to reference the input of my value, my issue was solved:
state = {
myObject: {
inputValue: ''
}
}
When you use onChange={this.onFieldChange('name').bind(this)} in your input you must declare your state empty string as a value of property field.
incorrect way:
this.state ={
fields: {},
errors: {},
disabled : false
}
correct way:
this.state ={
fields: {
name:'',
email: '',
message: ''
},
errors: {},
disabled : false
}
If the props on your component was passed as a state, put a default value for your input tags
<input type="text" placeholder={object.property} value={object.property ? object.property : ""}>
Set a value to 'name' property in initial state.
this.state={ name:''};
An update for this. For React Hooks use const [name, setName] = useState(" ")
Simply create a fallback to '' if the this.state.name is null.
<input name="name" type="text" value={this.state.name || ''} onChange={this.onFieldChange('name').bind(this)}/>
This also works with the useState variables.
I believe my input is controlled since it has a value.
Now you can do this two ways the best way is to have a state key to each input with 1 onChange handler. If you have checkboxes you will need to write a separate onChange handler.
With a Class component you would want to write it like this 👇
import React from 'react';
export default class MyForm extends React.Component {
constructor(props) {
super(props);
this.state = {
myFormFields: {
name: '',
dob: '',
phone: ''
}
}
this.onFormFieldChange = this.onFormFieldChange.bind(this)
}
// Always have your functions before your render to keep state batches in sync.
onFormFieldChange(e) {
// No need to return this function can be void
this.setState({
myFormFields: {
...this.state.myFormFields,
[e.target.name]: e.target.value
}
})
}
render() {
// Beauty of classes we can destruct our state making it easier to place
const { myFormFields } = this.state
return (
<form className="add-support-staff-form">
<input name="name" type="text" value={myFormFields.name} onChange={this.onFormFieldChange}/>
<input name="dob" type="date" value={myFormFields.dob} onChange={this.onFormFieldChange}/>
<input name="phone" type="number" value={myFormFields.phone} onChange={this.onFormFieldChange}/>
</form>
)
}
}
export default MyForm;
Hope that helps for a class but the most performative and what the newest thing the devs are pushing everyone to use is Functional Components. This is what you would want to steer to as class components don't intertwine well with the latest libraries as they all use custom hooks now.
To write as a Functional Component
import React, { useState } from 'react';
const MyForm = (props) => {
// Create form initial state
const [myFormFields, setFormFields] = useState({
name: '',
dob: '',
phone: ''
})
// Always have your functions before your return to keep state batches in sync.
const onFormFieldChange = (e) => {
// No need to return this function can be void
setFormFields({
...myFormFields,
[e.target.name]: e.target.value
})
}
return (
<form className="add-support-staff-form">
<input name="name" type="text" value={myFormFields.name} onChange={onFormFieldChange}/>
<input name="dob" type="date" value={myFormFields.dob} onChange={onFormFieldChange}/>
<input name="phone" type="number" value={myFormFields.phone} onChange={onFormFieldChange}/>
</form>
)
}
export default MyForm;
Hope this helps! 😎
In short, if you are using class component you have to initialize the input using state, like this:
this.state = { the_name_attribute_of_the_input: "initial_value_or_empty_value" };
and you have to do this for all of your inputs you'd like to change their values in code.
In the case of using functional components, you will be using hooks to manage the input value, and you have to put initial value for each input you'd like to manipulate later like this:
const [name, setName] = React.useState({name: 'initialValue'});
If you'd like to have no initial value, you can put an empty string.
In my case component was rerendering and throwing A component is changing an uncontrolled input of type checkbox to be controlled error. It turned out that this behaviour was a result of not keeping true or false for checkbox checked state (sometimes I got undefined). Here what my faulty component looked like:
import * as React from 'react';
import { WrappedFieldProps } from 'redux-form/lib/Field';
type Option = {
value: string;
label: string;
};
type CheckboxGroupProps = {
name: string;
options: Option[];
} & WrappedFieldProps;
const CheckboxGroup: React.FC<CheckboxGroupProps> = (props) => {
const {
name,
input,
options,
} = props;
const [value, setValue] = React.useState<string>();
const [checked, setChecked] = React.useState<{ [name: string]: boolean }>(
() => options.reduce((accu, option) => {
accu[option.value] = false;
return accu;
}, {}),
);
React.useEffect(() => {
input.onChange(value);
if (value) {
setChecked({
[value]: true, // that setChecked argument is wrong, causes error
});
} else {
setChecked(() => options.reduce((accu, option) => {
accu[option.value] = false;
return accu;
}, {}));
}
}, [value]);
return (
<>
{options.map(({ value, label }, index) => {
return (
<LabeledContainer
key={`${value}${index}`}
>
<Checkbox
name={`${name}[${index}]`}
checked={checked[value]}
value={value}
onChange={(event) => {
if (event.target.checked) {
setValue(value);
} else {
setValue(undefined);
}
return true;
}}
/>
{label}
</LabeledContainer>
);
})}
</>
);
};
To fix that problem I changed useEffect to this
React.useEffect(() => {
input.onChange(value);
setChecked(() => options.reduce((accu, option) => {
accu[option.value] = option.value === value;
return accu;
}, {}));
}, [value]);
That made all checkboxes keep their state as true or false without falling into undefined which switches control from React to developer and vice versa.
For people using Formik, you need to add a default value for the specific field name to the form's initialValues.
This generally happens only when you are not controlling the value of the filed when the application started and after some event or some function fired or the state changed, you are now trying to control the value in input field.
This transition of not having control over the input and then having control over it is what causes the issue to happen in the first place.
The best way to avoid this is by declaring some value for the input in the constructor of the component.
So that the input element has value from the start of the application.
Please try this code
import React from "react";
class MyForm extends React.Component {
constructor(props) {
super(props);
this.state = { name: "" };
this.onFieldChange = this.onFieldChange.bind(this);
}
onFieldChange(e) {
this.setState({[e.target.name]: e.target.value});
}
render() {
return (
<form className="add-support-staff-form">
<input name="name" type="text" value={this.state.name} onChange={this.onFieldChange} />
</form>
);
}
}
export default MyForm;
In my case there was spell mistake while setting the state which was causing defined value to be undefined.
This is my default state with value
const [email, setEmail] = useState(true);
my mistake was-
setEmail(res?.data?.notificationSetting.is_email_notificatio);
and the solution is -
setEmail(res?.data?.notificationSetting.is_email_notification);
last char was missing
I had the same issue with type='radio'
<input type='radio' checked={item.radio} ... />
the reason was that item.radio is not always true or false, but rather true or undefined, for example. Make sure it’s always boolean, and the problem will go away.
<input type='radio' checked={!!item.radio} ... />
source
For dynamically setting state properties for form inputs and keeping them controlled you could do something like this:
const inputs = [
{ name: 'email', type: 'email', placeholder: "Enter your email"},
{ name: 'password', type: 'password', placeholder: "Enter your password"},
{ name: 'passwordConfirm', type: 'password', placeholder: "Confirm your password"},
]
class Form extends Component {
constructor(props){
super(props)
this.state = {} // Notice no explicit state is set in the constructor
}
handleChange = (e) => {
const { name, value } = e.target;
this.setState({
[name]: value
}
}
handleSubmit = (e) => {
// do something
}
render() {
<form onSubmit={(e) => handleSubmit(e)}>
{ inputs.length ?
inputs.map(input => {
const { name, placeholder, type } = input;
const value = this.state[name] || ''; // Does it exist? If so use it, if not use an empty string
return <input key={name} type={type} name={name} placeholder={placeholder} value={value} onChange={this.handleChange}/>
}) :
null
}
<button type="submit" onClick={(e) => e.preventDefault }>Submit</button>
</form>
}
}